1. Technical Field
The present invention relates to an ignition system having an improved high voltage diode implementation for preventing a spark-on-make condition in an internal combustion engine.
2. Description of the Related Art
A conventional automotive ignition system includes a spark plug for each combustion chamber of an engine, at least one ignition coil and at least one device adapted to selectively charge the coil(s) and cause the energy stored in the coil(s) to be discharged through the spark plugs in a timed manner. As a result, a spark is generated and ignition of a fuel-air mixture in each combustion chamber occurs at a specified timing.
When charging of the coil is initiated, however, a transient voltage is created across the secondary winding of the ignition coil, which is connected to the spark plug. In some situations, this transient voltage may be high enough to create a spark at the spark plug. This kind of sparking event is commonly referred to as a spark-on-make event or condition because historically it would occur when the breaker points of the ignition system made contact to commence charging of the ignition coil. The term xe2x80x9cspark-on-makexe2x80x9d, as used in this disclosure, however, is not limited to situations where conventional breaker points are used. To the contrary, it refers to any situation where initiation of coil or ignition system charging causes a spark at one or more of the spark plugs. This kind of sparking event, however, is undesirable because it is not timed for proper engine operation. It can cause severe damage to engine components.
Recent advances in technology have made it more practical and desirable in some situations to provide a coil-per-cylinder ignition arrangement (i.e., wherein a coil is provided for each cylinder of the engine). While the coil-per-cylinder arrangements provide some benefits and advantages, the spark-on-make condition is more likely to occur in such an arrangement. The spark-on-make conditions or events, as a result, tend to detract from the benefits achieved by providing a coil for each cylinder.
One approach taken in the art to suppress and/or avoid a spark-on-make condition involves providing a high voltage (HV) diode that is used to permit the flow of current in one direction to the spark plug (i.e., to allow flow of the spark current) but not in the reverse direction. This configuration allows the coil to be discharged after sufficient and at the proper time, while preventing application of the transient voltage created during initiation of the charging process. For example, U.S. Pat. No. 5,586,542 issued to Taruya et al. disclose an ignition coil composed of a primary coil and a secondary coil wherein a high-tension diode for preventing faulty operation is inserted to the output terminal of the secondary coil. However, in terms of a conventional 14 volt automotive system, a typical xe2x80x9cmakexe2x80x9d voltage ranges between about 1500 to 2000 volts. The conventional approach of using a high voltage diode is effective with the use of a single, conventional 3 kV diode. It is known to place such diodes on either the high voltage end (such as disclosed in Taruya et al.) or the low voltage end of the ignition coil secondary. The foregoing approach, however, has limitations.
In particular, a 42 volt standard has been proposed for both Europe and the United States for automotive vehicle electrical systems. In such a 42 volt system, the xe2x80x9cmakexe2x80x9d voltages will be approximately three times higher than that of a 14 volt system. While it may be possible to simply increase the voltage rating of the above-mentioned 3 kV diode to 6 kV, the 6 kV diode has an increased length compared to a 3 kV diode, and would therefore increase difficulties in packaging, particularly if such a 6 kV diode were placed at the high voltage end of the secondary winding, as would simply including two 3 kV diodes in series.
There is therefore a need to provide an improved ignition system that minimizes or eliminates a spark-on-make condition, as well as minimizing or eliminating one or more of the shortcomings as set forth above.
One object of the present invention is to provide a solution to one or more of the above-identified problems. The invention involves packaging one HV diode at both ends of a secondary winding of an ignition coil assembly. One advantage of the present invention is that it allows for suppression of a spark-on-make condition, particularly for increased voltage systems, such as a 42 volt automotive electrical system, without increasing the number of components, the number of connections, or the number of assembly operations and the manufacture of an ignition apparatus, all as described in detail herein.
An ignition coil assembly is provided in accordance with the present invention, and includes a transformer having a core, a primary winding, and a secondary winding, as well as first and second diodes. The secondary winding has a high voltage end and a low voltage end. The first diode is disposed between the low voltage end and a low voltage node. In a preferred embodiment, the low voltage node comprises either a supply node (e.g., an automotive system supply) or a ground node. The second diode is disposed between the high voltage end and a connector associated with the ignition coil assembly configured for electrical connection to a spark plug.
A method of making an ignition coil assembly is also presented.